<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8">
        <meta http-equiv="X-UA-Compatible" content="IE=edge">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <title>Document</title>

        <style>
            .box1 {
                width: 200px;
                height: 200px;
                background-color: #bfa;
            }

            /* .box1::before {
                content: '';
                display: inline-block;
            } */

            .box2 {
                width: 100px;
                height: 100px;
                background-color: orange;
                margin-top: 100px;
            }


            /* 
                (非常好用,强烈推荐)
                clearfix这个样式可以同时解决高度塌陷和外边距重叠的问题
                当你遇到这些问题时,直接使用clearfix这个类即可
            */
            .clearfix::before,
            .clearfix::after {
                content: '';
                display: table;
                clear: both;
            }
        </style>
    </head>
    <body>
        <div class="box1 clearfix">
            <div class="box2"></div>
        </div>
    </body>
</html>